1. Field of the Invention
This invention relates to a memory card having a nonvolatile memory and a host device thereof and more particularly to a memory card having a flash memory and a host device thereof.
2. Description of the Related Art
As a data storage medium used for, for example, a digital camera or mobile telephone, a small-sized memory card is developed. The memory card can transfer data with respect to a host device such as a digital camera or mobile telephone in a state in which the memory card is attached to the host device. As one type of the memory card, an SD™ (secure digital) memory card using a flash memory in the storage circuit is known.
For the SD™ memory card, recently, it is required to enhance the write/read operation speed and it is also required to enhance the transfer speed of a bus contained in the memory card. In the SD™ memory card, enhancement (25 MHz→50 MHz) of the transfer clock rate of the bus is defined by the “Physical Specifications, Ver. 1.1” and a higher-speed data transfer operation can be attained.
It is supposed that an even higher-speed data transfer operation is required in future, but in order to satisfy the above requirement, means for (1) further enhancing the transfer clock rate, (2) increasing the transfer data width (at present, 4-bit parallel at maximum) or the like is taken into consideration.
However, in the case of (1) enhancement of the transfer clock rate, there occurs a problem that an influence by noise increases or definition of timings becomes severe due to the enhanced clock rate. Further, in the case of (2) an increase in the bus width, there occurs a problem that the cost rises since the number of input/output pins of the SD™ memory card is increased.
As the related technique of the above type, the technique for efficiently transfer stream data on the bus is disclosed (refer to Jpn. Pat. Appln. KOKAI Publication No. 2001-216258).